Iburg is a ruined hill castle in Westphalia. It was build around the 8th century, dating back to the time of Charlemagne and his war with the Saxons. Today it is a popular day-trip destination and the tower, named after Charlemagne (Kaiser Karl Turm), can be climbed for beautiful views.
It is likely that the castle was originally erected by Saxons as a fortified stronghold but once conquered Charlemagne build a chapel within its confines to honour St.Peter, which he eventually gifted to the Arch-Diocese of Paderborn. From 1134 a monastery briefly used the castle before the Bishop of Paderborn fortified it to become a stronger military fortress in the late 12th century. The Iburg never saw much action, however, and slipped from importance until the 15th century, when Otto of Braunschweig destroyed it. The castle was not restored and the close-by city of Bad Driburg inherited the holdings.
First archeological surveys were undertaken on 1900 and gradually the ruins where freed and restored to serve as tourist attraction.
References:The Clementinum is a historic complex of buildings in Prague. Until recently the complex hosted the National, University and Technical libraries, the City Library also being located nearby on Mariánské Náměstí. The Technical library and the Municipal library have moved to the Prague National Technical Library at Technická 6 since 2009. It is currently in use as the National Library of the Czech Republic.
Its history dates from the existence of a chapel dedicated to Saint Clement in the 11th century. A Dominican monastery was founded in the medieval period, which was transformed in 1556 to a Jesuit college. In 1622 the Jesuits transferred the library of Charles University to the Klementinum, and the college was merged with the University in 1654. The Jesuits remained until 1773, when the Klementinum was established as an observatory, library, and university by the Empress Maria Theresa of Austria.